Due to the reduction of CYP46A1 in AD brain, single nucleotide polymorphisms in CYP46A1 have been studied, in which CYP46A1 introns 1 (rs7157609) and 3 (rs4900442) were found to increase the risk of AD (Kölsch et al., 2009). Here, CYP46A1 is linked to Alzheimer disease.